7.6 Tier IV Volatile Emissions Risk Assessment

Appendix F addresses volatile emissions from an exposed sediment. The

predictive equations for modeling these emissions consider a uniformly

contaminated dredged material that is freshly deposited and dewatered in a CDF.

Evaporation begins from the upper segments of the dredged material and as

depletion of contaminants occurs, the flux to air decreases to small values.

The detailed calculations for determining on- and off-site exposure

concentrations are given in Appendix F. The model is part of the Automated

Dredging and Disposal Alternatives Modeling System (ADDAMS) suite of

models currently available through ERDC at: http://www.wes.army.mil/el/

elmodels/index.html#addams.

7.6 Tier IV Volatile Emissions Risk Assessment

7.6.1 Evaluation

Tier IV is intended to answer whatever specific, well-defined technical

questions may remain unanswered after thorough evaluation in earlier tiers. If

earlier tiers are used properly, Tier IV should rarely be necessary.

By the nature of the tiered evaluation approach, any technical questions that

remain unresolved after Tier III can best be answered by a detailed, case-specific

evaluation. By their very nature, detailed case-specific evaluations are not

amenable to the kind of generic guidance that can be presented in a national

manual. They require individual design to address unique technical questions

under site-specific conditions.

The best approach for Tier IV is usually a case-specific risk assessment.

Detailed guidance for conducting risk assessments for CDFs in Tier IV can be

found in Cura, Wickwire, and McArlde (in preparation). The information

generated in Tiers I through III should be used to the maximum extent technically

justified throughout the Tier IV risk assessment.

7.6.2 Tier IV - Volatile Emissions Decision

After consideration of the Tier IV effluent evaluation results, all relevant

information is available and no further evaluation is possible. One of the

following conclusions is reached.

1. No management actions are required.

2. Management actions should be considered. A decision to implement

management actions for emissions, such as capping or treatment, may

require more detailed information prior to design of such actions.

7-12

Chapter 7

Guidance for Evaluation of Volatile Emissions